1. Field of the Invention
The present invention relates to a sucker rod pump for pumping fluids, such as hydrocarbons, from an underground formation to the earth's surface, and more particularly, but not by way of limitation, to an improved downhole pump assembly for pumping fluids while minimizing the conditions of “gas lock” and “gas pound.”
2. Description of Related Art
Sucker rod pumps are often used when the natural pressure of an oil and gas formation is not sufficient to lift the oil to the surface of the earth. Sucker rod pumps operate by admitting fluid from the formation into a tubing and then lifting the fluid to the surface. To accomplish this, the sucker rod pump contains, among others, four elements:                (1) a pump or working barrel, (2) a plunger which travels in an up and down motion inside the pump barrel, (3) a standing valve positioned near the lower end of the pump barrel and (4) a traveling valve that is attached to and travels with the plunger.        
A chamber is formed inside the pump barrel between the standing valve and the traveling valve. The standing valve allows fluid to flow into the chamber but does not allow fluid to flow out of the chamber. The traveling valve allows fluid to flow out of the chamber, but not into the chamber.
When the fluid that the sucker rod pump is pumping is substantially all liquids, the plunger is mechanically made to move up and down in a reciprocating motion. On the upstroke of a pumping cycle, where the plunger is moved upward, the hydrostatic pressure of the fluid above the traveling valve causes the traveling valve to close. The upward motion of the plunger also causes a negative fluid pressure to develop inside the chamber thereby causing the standing valve to open and to admit fluid from the formation into the chamber.
At the end of the upstroke, the chamber is filled with liquid from the formation. When the plunger begins the downstroke, the pressure in the chamber becomes positive which causes the standing valve to close. Because liquids are substantially incompressible, the pressure in the chamber rapidly increases to a pressure greater than the fluid column pressure above the traveling valve. When the fluid pressure in the chamber becomes greater than the fluid column pressure above the traveling valve, the traveling valve opens and fluid passes by the traveling valve where it is able to be lifted by the sucker rod pump on the upstroke.
When the fluid being pumped by the sucker rod pump is a mixture of gas and liquid, problems may be encountered. During the downstroke, the standing valve closes normally as the plunger compresses the gas and liquid in the chamber. However, the traveling valve does not open until the chamber pressure becomes greater than the hydrostatic pressure above the traveling valve. If the fluid contains a significant amount of gas, the traveling valve may not open at all, even as the plunger reaches the bottom of the downstroke. This condition results in a “gas lock.” When the plunger compresses the gas and collides with the liquid, the collision generates a shock wave and is referred to as “gas pound.” The shock wave causes the traveling valve to open quickly and this can cause damage to the traveling valve and to the tubing in the well.
To this end, a need exists for an improved sucker rod pump that prevents the formation of gas lock and gas pound. It is to such an improved sucker rod pump that the present invention is directed.